This invention relates to an oil seal arrangement for use with an oil pump used in a vehicle brake actuator or a shock absorber.
As oil pump assemblies used in vehicle brake actuators, a gear pump is disclosed in JP patent publication 2000-9058 or 2001-80498. The gear pump will be described with reference to FIGS. 1 and 2. (Note that FIGS. 1 and 2 show an oil seal arrangement embodying the invention.)
This gear pump assembly includes a housing H formed with suction ports 1 through which oil a is drawn into the housing H and discharge ports 2 through which pressurized oil a is discharged. In the housing H, a rotary shaft 3 driven by a motor M extends in the axial direction of the housing H. The rotary shaft 3 carries a plurality of pump units 10 arranged in the axial direction of the shaft 3. Each pump unit 10 comprises an inner rotor 4 fixed to the rotary shaft 3, and an outer rotor 5 disposed in a casing 7d or 7e so as to be rotatable and eccentric to and in mesh with the inner rotor 4.
In order to prevent brake oil a pressurized in the pump units 10 from leaking to outside through gaps between the rotary shaft 3 and cylinders 7a and 7c, high-pressure oil seals 8 are disposed therebetween. Further, in order to prevent leak of such pressurized brake fluid even if the high-pressure seals 8 fail, a low-pressure seal 9 is provided between an axially outer portion of the cylinder 7c and the rotary shaft 3.
As the inner and outer rotors of each pump unit 10 rotate, positive pressure and negative pressure are alternately produced in each chamber defined in the pump units. Negative pressure tends to draw outer air into the pump units 10 through the high-pressure seals 8. Air drawn into the pump units will have undue influence on the function of the brake actuator.
An object of this invention is to provide an oil seal arrangement for such a gear pump which includes, besides the high-pressure seals and low-pressure seal, additional sealing means that can positively prevent infiltration of air into the pumps under negative pressure produced in the pumps.